1. Field of the Invention
The present invention relates to a zoom lens system for suitable use in an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcast camera, or a surveillance camera, or an image pickup apparatus such as a camera using a silver film, and to a camera including the zoom lens system.
2. Description of the Related Art
In recent years, image pickup apparatuses, such as a video camera, a digital still camera, a broadcast camera, and a surveillance camera using a solid-state image pickup element, and a camera using a silver film, have been sophisticated and reduced in total size.
As an image taking optical system for use in the image pickup apparatuses, there is a demand for a zoom lens system having a long total length, a compact size, a high zoom ratio, and a high resolving power.
A positive lead type zoom lens system is known as a zoom lens system that meets this demand. In a positive lead type zoom lens system, a lens unit having a positive refractive power is provided on an object side.
As a positive lead type zoom lens system, a four-unit zoom lens system is known which includes, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power.
Japanese Patent Laid-Open Nos. 2001-042215 (US counterpart: U.S. Pat. No. 6,633,437) and 2004-199000 disclose four-unit zoom lens systems having a simple structure in which a first lens unit is formed by one lens element.
Japanese Patent Laid-Open No. 2006-235062 (US counterpart: U.S. Pat. No. 7,167,320) also discloses a four-unit zoom lens system having a simple structure in which a first lens unit is composed of one negative lens element and one positive lens element.
Japanese Patent Laid-Open Nos. 2006-308649 (US counterpart: U.S. Pat. No. 7,333,274) and 2000-347102 (US counterpart: U.S. Pat. No. 6,867,925) also disclose four-unit zoom lens systems in which a first lens unit is formed by a cemented lens of a negative lens element and a positive lens element, and a second lens unit includes three negative lens elements and one positive lens element.
Japanese Patent Laid-Open No. 2006-189627 (US counterpart: US Patent Application Publication No. 2006/0146417 A1) discloses a four-unit zoom lens system in which a third lens unit is moved in a direction having a component perpendicular (orthogonal) to the optical axis in order to correct image blur caused by vibration of the zoom lens system.
In general, in order to reduce the total size of the zoom lens system while maintaining a predetermined zoom ratio, the number of lens elements is reduced while increasing the refractive powers of the lens units in the zoom lens system.
In this case, however, when the thicknesses of the lens elements increase with the increase in refractive power of the lens surfaces, it becomes more difficult to correct various aberrations.
In the above-described four-unit zoom lens systems, in order to obtain a high optical performance while ensuring a high zoom ratio and a reduced total size, it is important to appropriately set the refractive powers and lens configurations of the lens units and the moving conditions of the lens units during zooming.
In particular, it is important to appropriately set the moving conditions of the lens units during zooming and refractive powers and lens configurations of the first and second lens units.
If the above-described factors are not appropriately set, it is significantly difficult to obtain a high optical performance over the entire zoom range while ensuring a reduced diameter of the foremost lens and a high zoom ratio.